Actuation for a focus adjusting head mounted display

ABSTRACT

A head mounted display (HMD) includes an electronic display configured to display a virtual scene to a user, an optics block, an eye tracking system, and a varifocal actuation that mechanically changes a distance between the optics block and the electronic display. The varifocal actuation block is configured to change a location of an image plane of the HMD and includes a motor, a power screw coupled to the actuating motor configured to turn responsive to actuation of the motor, and a nut sled on the power screw that is coupled to the electronic display. The nut sled is configured to move back and forth along a length of the power screw responsive to the power screw being turned by the motor that results in movement of the electronic display relative to the optics block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 17/214,101, filed Mar. 26, 2021, which is a continuation of U.S.application Ser. No. 16/675,993, filed Nov. 6, 2019, now U.S. Pat. No.10,994,196, which is a continuation of U.S. application Ser. No.15/862,456, filed Jan. 4, 2018, now U.S. Pat. No. 10,610,775, whichclaims the benefit of U.S. Application No. 62/442,393, filed Jan. 4,2017, each of which is incorporated by reference in their entirety.

BACKGROUND

The present disclosure generally relates to enhancing images fromelectronic displays, and specifically to a mechanism for varying alocation of the image plane to enhance the images.

A head mounted display (HMD) can be used to simulate virtualenvironments. For example, stereoscopic images are be displayed on anelectronic display inside the HMD to simulate the illusion of depth andhead tracking sensors estimate what portion of the virtual environmentis being viewed by the user. However, conventional HMDs are often unableto compensate for vergence and accommodation conflicts when renderingcontent, which may cause visual fatigue and nausea in users.

SUMMARY

A head mounted display (HMD) includes an electronic display screenconfigured to display a virtual scene to a user wearing the HMD, anoptics block that directs image light from the electronic displaytowards an eye of a user, an eye tracking system configured to determinean eye position of the user, and a varifocal actuation block (e.g., anelement that mechanically changes a distance between a lens system inthe optics block and the electronic display element). The varifocalactuation block, in various embodiments, automatically adjust the focusof the optics block. For example, a three-dimensional (3D) virtual sceneis presented on an electronic display screen of the HMD and a locationof an image plane is adjusted using a varifocal actuation block based ona location or object within the virtual scene where the user is looking.The eye tracking system includes an infrared camera and a mirrorpositioned at an angle in optical series with the one or more lenses ofthe optics block and the electronic display screen to reflect infraredlight from an eye of the user wearing the HMD to the infrared camera.

The varifocal actuation block is configured to change a location of theimage plane (e.g., may adjust focus of the optics block and/or adjust alocation of one or more elements of the optics block relative to theelectronic display screen) based on the eye position of the user andincludes an actuating motor, a power screw coupled to the actuatingmotor that is configured to turn in response to actuation of theactuating motor, and a nut sled on the power screw that is coupled tothe electronic display screen. The nut sled is configured to move backand forth along a length of the power screw in response to the powerscrew being turned by the actuating motor that results in movement ofthe electronic display screen relative to the optics block.

An encoder, in communication with the eye tracking system and thevarifocal actuation block, receives the eye position determined by theeye tracking system, determines the focal length and/or location of theoptics block that provides focus for the eye position, and provides aninstruction to the varifocal actuation block to move the electronicdisplay screen to a position providing focus for the eye positiondetermined by the eye tracking system.

The optics block, in one embodiment, is fixed to a housing of the HMDand the varifocal actuation block moves the electronic display screenrelative to the optics block along an optical axis of the optics blockand the electronic display screen moves relative to the optics blockalong the optical axis of the optics block via guide pins attached tothe electronic display screen where a male end of each guide pin coupleswith a female end of a corresponding guide pin fixed to the opticsblock. Additionally, a bracket holding the motor and the power screw ismounted to the housing of the HMD and the nut sled on the power screwcoupled to the electronic display screen moves the electronic displayscreen relative to the optics block to change the image plane for a userviewing content displayed on the electronic display screen at an exitpupil of the HMD.

The infrared camera, in one embodiment, is located off-axis at an anglerelative to optical axis and the hot mirror is positioned at an angle toreflect the infrared light from the eye of the user wearing the HMD tothe infrared camera off-axis. Thus, the hot mirror is transparent tovisible light to allow the light from electronic display to pass throughto the user unimpeded while reflecting the IR light with the position ofthe eye of the user to infrared camera. The infrared camera, in oneembodiment, captures infrared light reflected from a retina of the eyeof the user and the eye tracking system determines the position of theeye of the user using the infrared light reflected from the retina. Theencoder then uses the position of the eye to determine a vergence depthcorresponding to a virtual depth in the virtual scene at which the eyesof the user are focused.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example virtual reality system, in accordance with atleast one embodiment.

FIG. 2 shows a diagram of a head mounted display, in accordance with atleast one embodiment.

FIG. 3 shows a cross section of a head mounted display including acamera for tracking eye position, in accordance with at least oneembodiment.

FIGS. 4A and 4B show an example process for adjusting the focal distanceof a head mounted display by varying the distance between a displayscreen and the optics block using a varifocal actuation block, inaccordance with at least one embodiment.

FIGS. 5A-5C show example portions of a head mounted display thatincludes a varifocal actuation block using a power screw, in variousembodiments.

FIGS. 6A-6B show example portions of a head mounted display thatincludes a varifocal actuation block using a cam and roller, in variousembodiments.

FIG. 7 shows an example portion of a head mounted display that includesa varifocal actuation block using a face cam of varying thickness thatpushes against push contact roller to move the electronic display, inone embodiment.

FIG. 8 shows an example portion of a head mounted display that includesa varifocal actuation block using a pivoting arm to move a displaybracket supporting an electronic display, in one embodiment.

FIG. 9A shows an example portion of a head mounted display that includesa varifocal actuation block using a rolling or sliding CAM contactsurfaces to induce translation of an electronic display relative to anoptics block, in one embodiment.

FIGS. 9B-9C show example portions of a head mounted display thatincludes a varifocal actuation block using a gear and rackimplementation, in various embodiments.

FIGS. 10A-10D show example portions of a head mounted display thatincludes a varifocal actuation block using a cable or belt drive withone or more pulleys, and a friction drive wheel in various embodiments.

FIG. 11 shows an example portion of a head mounted display that includesa threaded ring that engages a threaded portion of an end of an opticsblock to telescopically move an electronic display, in one embodiment.

FIG. 12 shows an example portion of a head mounted display that includesa varifocal actuation block using a gear threaded actuator attached to acenter of an electronic display to push the electronic display frombehind, in one embodiment.

FIGS. 13A-13B show example portions of a head mounted display thatincludes a varifocal actuation block using a solenoid or Voice CoilActuator (VCA) as a motor to drive movement of an electronic display, invarious embodiment.

FIG. 13C shows an example portion of a head mounted display thatincludes a varifocal actuation block using a voice coil as a motor todrive movement of an electronic display, in one embodiment.

FIG. 14 shows an example portion of a head mounted display that includesa varifocal actuation block using alternating north-south poled shaftwith solenoid-like driving coil, in one embodiment.

FIGS. 15A-15C shows an example portion of a head mounted display thatincludes a varifocal actuation block using Piezo bending and pneumaticactuation to move an electronic display, in various embodiments.

FIGS. 16A-16D shows an example portion of a head mounted display thatincludes a varifocal actuation block includes interpupillary distanceadjustment, in various embodiments.

FIG. 17A shows an example portion of a head mounted display thatincludes a varifocal actuation block using a Flexure based guidancemethod, in one embodiment.

FIG. 17B shows a side cut view of a varifocal actuation block usinganother Flexure based guidance method, in one embodiment.

FIG. 17C shows a perspective view of a varifocal actuation block usingthe Flexure based guidance method of FIG. 17B.

FIG. 17D shows an example Flexure that can be used to guide movement ofan electronic display, in various embodiments.

FIG. 17E shows a perspective view of a varifocal actuation block usingthe Flexure based guidance method of FIGS. 17B-17D in operation.

FIG. 18 shows an example portion of a head mounted display that includesa varifocal actuation block using a pin and shaft guidance method, invarious embodiments.

FIGS. 19A-19B shows an example portion of a head mounted displayillustrating one guidance implementation for a varifocal actuationblock, in various embodiments.

FIG. 20 shows an example portion of a head mounted display that includesa varifocal actuation block using a scissor linkage method, in oneembodiment.

FIGS. 21A-21B shows an example portion of a head mounted display thatincludes a varifocal actuation block using a Sarrus linkage guidancemethod, in various embodiment.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

Varifocal Actuation Overview

A varifocal system provides dynamic adjustment of the focal distance ofa head mounted display (HMD) to keep a user's eyes in a zone of comfortas vergence and accommodation change. The system uses an eye tracker todetermine a vergence depth corresponding to where the user is lookingand adjusts the focus to ensure image is in focus at the determinedfocal plane. The system, in one implementation, physically changes thedistance between an electronic display and optical block of the HMD bymoving the electronic display, optical block, or both using variousactuation devices, guidance system, and encoder mechanisms describedherein.

System Overview

FIG. 1 shows varifocal system 100 in which a head-mounted display (HMD)101 operates. Varifocal system 100 may be for use as a virtual reality(VR) system, an augmented reality (AR) system, a mixed reality (MR)system, or some combination thereof. In this example, the varifocalsystem 100 includes HMD 101, imaging device 160, and I/O interface 170,which are each coupled to console 150. While FIG. 1 shows a single HMD101, a single imaging device 160, and a single I/O interface 170, inother embodiments, any number of these components may be included in thesystem. For example, there may be multiple HMDs each having anassociated I/O interface 170 and being monitored by one or more imagingdevices 160, with each HMD 101, I/O interface 170, and imaging devices160 communicating with the console 150. In alternative configurations,different and/or additional components may also be included in thesystem environment.

HMD 101 presents content to a user. Example content includes images,video, audio, or some combination thereof. Audio content may bepresented via a separate device (e.g., speakers and/or headphones)external to HMD 101 that receives audio information from HMD 101,console 150, or both. HMD 101 includes electronic display 102, opticsblock 104, varifocal actuation block 106, focus prediction module 108,eye tracking module 110, vergence processing module 112, one or morelocators 114, internal measurement unit (IMU) 116, head tracking sensors118, and scene rendering module 120.

Optics block 104 directs light from electronic display 102 to an exitpupil for viewing by a user using one or more optical elements, such asapertures, Fresnel lenses, convex lenses, concave lenses, filters, andso forth, and may include combinations of different optical elements. Insome embodiments, one or more optical elements in optics block 104 mayhave one or more coatings, such as anti-reflective coatings.Magnification of the image light by optics block 104 allows electronicdisplay 102 to be physically smaller, weigh less, and consume less powerthan larger displays. Additionally, magnification of the image light mayincrease a field of view of the displayed content. For example, thefield of view of the displayed content is such that the displayedcontent is presented using almost all (e.g., 150 degrees diagonal), andin some cases all, of the user's field of view.

Optics block 104 may be designed to correct one or more optical errors.Examples of optical errors include: barrel distortion, pincushiondistortion, longitudinal chromatic aberration, transverse chromaticaberration, spherical aberration, comatic aberration, field curvature,astigmatism, and so forth. In some embodiments, content provided toelectronic display 102 for display is pre-distorted, and optics block104 corrects the distortion when it receives image light from electronicdisplay 102 generated based on the content.

Varifocal actuation block 106 includes a varifocal actuation block thatcauses optics block 104 to vary the focal distance of HMD 101 to keep auser's eyes in a zone of comfort as vergence and accommodation change.In one embodiment, varifocal actuation block 106 physically changes thedistance between electronic display 102 and optical block 104 by movingelectronic display 102 or optical block 104 (or both), as will beexplained further with respect to FIGS. 4A-21B. Additionally, moving ortranslating two lenses relative to each other may also be used to changethe focal distance of HMD 101. Thus, varifocal actuation block 106 mayinclude actuators or motors that move electronic display 102 and/oroptical block 104 to change the distance between them. Varifocalactuation block 106 may be separate from or integrated into optics block104 in various embodiments.

Each state of optics block 104 corresponds to a focal distance of HMD101 or to a combination of the focal distance and eye position relativeto optics block 104 (as discussed further below). In operation, opticsblock 104 may move in a range of ˜5 10 mm with a positional accuracy of˜5-10 μm for a granularity of around 1000 focal distances, correspondingto 1000 states of optics block 104. Any number of states could beprovided; however, a limited number of states accommodate thesensitivity of the human eye, allowing some embodiments to include fewerfocal distances. For example, a first state corresponds to a focaldistance of a theoretical infinity meters (0 diopter), a second statecorresponds to a focal distance of 2.0 meters (0.5 diopter), a thirdstate corresponds to a focal distance of 1.0 meters (1 diopter), afourth state corresponds to a focal distance of 0.5 meters (1 diopter),a fifth state corresponds to a focal distance of 0.333 meters (3diopter), and a sixth state corresponds to a focal distance of 0.250meters (4 diopter). Varifocal actuation block 106, thus, sets andchanges the state of optics block 104 to achieve a desired focaldistance.

Focus prediction module 108 is an encoder including logic that tracksthe position or state of optics block 104 to predict to one or morefuture states or locations of optics block 104. For example, focusprediction module 108 accumulates historical information correspondingto previous states of optics block 104 and predicts a future state ofoptics block 104 based on the previous states. Because rendering of avirtual scene by HMD 101 is adjusted based on the state of optics block104, the predicted state allows scene rendering module 120, furtherdescribed below, to determine an adjustment to apply to the virtualscene for a particular frame. Accordingly, focus prediction module 108communicates information describing a predicted state of optics block104 for a frame to scene rendering module 120. Adjustments for thedifferent states of optics block 104 performed by scene rendering module120 are further described below.

Eye tracking module 110 tracks an eye position and eye movement of auser of HMD 101. A camera or other optical sensor inside HMD 101captures image information of a user's eyes, and eye tracking module 110uses the captured information to determine interpupillary distance,interocular distance, a three-dimensional (3D) position of each eyerelative to HMD 101 (e.g., for distortion adjustment purposes),including a magnitude of torsion and rotation (i.e., roll, pitch, andyaw) and gaze directions for each eye. In one example, infrared light isemitted within HMD 101 and reflected from each eye. The reflected lightis received or detected by the camera and analyzed to extract eyerotation from changes in the infrared light reflected by each eye. Manymethods for tracking the eyes of a user can be used by eye trackingmodule 110. Accordingly, eye tracking module 110 may track up to sixdegrees of freedom of each eye (i.e., 3D position, roll, pitch, and yaw)and at least a subset of the tracked quantities may be combined from twoeyes of a user to estimate a gaze point (i.e., a 3D location or positionin the virtual scene where the user is looking). For example, eyetracking module 110 integrates information from past measurements,measurements identifying a position of a user's head, and 3D informationdescribing a scene presented by electronic display element 102. Thus,information for the position and orientation of the user's eyes is usedto determine the gaze point in a virtual scene presented by HMD 101where the user is looking.

Further, distance between a pupil and optics block 104 changes as theeye moves to look in different directions. The varying distance betweenpupil and optics block 104 as viewing direction changes is referred toas “pupil swim” and contributes to distortion perceived by the user as aresult of light focusing in different locations as the distance betweenpupil and optics block 104. Accordingly, measuring distortion adifferent eye positions and pupil distances relative to optics block 104and generating distortion corrections for different positions anddistances allows mitigation of distortion caused by “pupil swim” bytracking the 3D position of a user's eyes and applying a distortioncorrection corresponding to the 3D position of each of the user's eye ata given point in time. Thus, knowing the 3D position of each of a user'seyes allows for the mitigation of distortion caused by changes in thedistance between the pupil of the eye and optics block 104 by applying adistortion correction for each 3D eye position.

Vergence processing module 112 determines a vergence depth of a user'sgaze based on the gaze point or an estimated intersection of the gazelines determined by eye tracking module 110. Vergence is thesimultaneous movement or rotation of both eyes in opposite directions tomaintain single binocular vision, which is naturally and automaticallyperformed by the human eye. Thus, a location where a user's eyes areverged is where the user is looking and is also typically the locationwhere the user's eyes are focused. For example, vergence processingmodule 112 triangulates the gaze lines to estimate a distance or depthfrom the user associated with intersection of the gaze lines. The depthassociated with intersection of the gaze lines can then be used as anapproximation for the accommodation distance, which identifies adistance from the user where the user's eyes are directed. Thus, thevergence distance allows determination of a location where the user'seyes should be focused and a depth from the user's eyes at which theeyes are focused, thereby, providing information, such as an object orplane of focus, for rendering adjustments to the virtual scene.

In some embodiments, rather than provide accommodation for the eye at adetermined vergence depth, accommodation may be directly determined by awavefront sensor, such as a Shack-Hartmann wavefront sensor; hence, astate of optics block 104 may be a function of the vergence oraccommodation depth and the 3D position of each eye, so optics block 104brings objects in a scene presented by electronic display element 102into focus for a user viewing the scene. Further, vergence andaccommodation information may be combined to focus optics block 104 andto render synthetic depth of field blur.

Locators 114 are objects located in specific positions on HMD 101relative to one another and relative to a specific reference point onHMD 101. Locator 114 may be a light emitting diode (LED), a corner cubereflector, a reflective marker, a type of light source that contrastswith an environment in which HMD 101 operates, or some combinationthereof. Active locators 114 (i.e., an LED or other type of lightemitting device) may emit light in the visible band (˜380 nm to 750 nm),in the infrared (IR) band (˜750 nm to 1 mm), in the ultraviolet band (10nm to 380 nm), some other portion of the electromagnetic spectrum, orsome combination thereof.

Locators 114 can be located beneath an outer surface of HMD 101, whichis transparent to the wavelengths of light emitted or reflected bylocators 114 or is thin enough not to substantially attenuate thewavelengths of light emitted or reflected by locators 114. Further, theouter surface or other portions of HMD 101 can be opaque in the visibleband of wavelengths of light. Thus, locators 114 may emit light in theIR band while under an outer surface of HMD 101 that is transparent inthe IR band but opaque in the visible band.

IMU 116 is an electronic device that generates fast calibration databased on measurement signals received from one or more of head trackingsensors 118, which generate one or more measurement signals in responseto motion of HMD 101. Examples of head tracking sensors 118 includeaccelerometers, gyroscopes, magnetometers, other sensors suitable fordetecting motion, correcting error associated with IMU 116, or somecombination thereof. Head tracking sensors 118 may be located externalto IMU 116, internal to IMU 116, or some combination thereof.

Based on the measurement signals from head tracking sensors 118, IMU 116generates fast calibration data indicating an estimated position of HMD101 relative to an initial position of HMD 101. For example, headtracking sensors 118 include multiple accelerometers to measuretranslational motion (forward/back, up/down, left/right) and multiplegyroscopes to measure rotational motion (e.g., pitch, yaw, and roll).IMU 116 can, for example, rapidly sample the measurement signals andcalculate the estimated position of HMD 101 from the sampled data. Forexample, IMU 116 integrates measurement signals received from theaccelerometers over time to estimate a velocity vector and integratesthe velocity vector over time to determine an estimated position of areference point on HMD 101. The reference point is a point that may beused to describe the position of HMD 101. While the reference point maygenerally be defined as a point in space, in various embodiments,reference point is defined as a point within HMD 101 (e.g., a center ofthe IMU 130). Alternatively, IMU 116 provides the sampled measurementsignals to console 150, which determines the fast calibration data.

IMU 116 can additionally receive one or more calibration parameters fromconsole 150. As further discussed below, the one or more calibrationparameters are used to maintain tracking of HMD 101. Based on a receivedcalibration parameter, IMU 116 may adjust one or more IMU parameters(e.g., sample rate). In some embodiments, certain calibration parameterscause IMU 116 to update an initial position of the reference point tocorrespond to a next calibrated position of the reference point.Updating the initial position of the reference point as the nextcalibrated position of the reference point helps reduce accumulatederror associated with determining the estimated position. Theaccumulated error, also referred to as drift error, causes the estimatedposition of the reference point to “drift” away from the actual positionof the reference point over time.

Scene render module 120 receives content for the virtual scene fromengine 156 and provides the content for display on electronic display102. Additionally, scene render module 120 can adjust the content basedon information from focus prediction module 108, vergence processingmodule 112, IMU 116, and head tracking sensors 118. For example, uponreceiving the content from engine 156, scene render module 120 adjuststhe content based on the predicted state (i.e., eye position and focaldistance) of optics block 104 received from focus prediction module 108by adding a correction or pre-distortion into rendering of the virtualscene to compensate or correct for the distortion caused by thepredicted state of optics block 104. Scene render module 120 may alsoadd depth of field blur based on the user's gaze, vergence depth (oraccommodation depth) received from vergence processing module 112, ormeasured properties of the user's eye (e.g., 3D position of the eye,etc.). Additionally, scene render module 120 determines a portion of thecontent to be displayed on electronic display 102 based on one or moreof tracking module 154, head tracking sensors 118, or IMU 116, asdescribed further below.

Imaging device 160 generates slow calibration data in accordance withcalibration parameters received from console 150. Slow calibration dataincludes one or more images showing observed positions of locators 114that are detectable by imaging device 160. Imaging device 160 mayinclude one or more cameras, one or more video cameras, other devicescapable of capturing images including one or more locators 114, or somecombination thereof. Additionally, imaging device 160 may include one ormore filters (e.g., for increasing signal to noise ratio). Imagingdevice 160 is configured to detect light emitted or reflected fromlocators 114 in a field of view of imaging device 160. In embodimentswhere locators 114 include passive elements (e.g., a retroreflector),imaging device 160 may include a light source that illuminates some orall of locators 114, which retro-reflect the light towards the lightsource in imaging device 160. Slow calibration data is communicated fromimaging device 160 to console 150, and imaging device 160 receives oneor more calibration parameters from console 150 to adjust one or moreimaging parameters (e.g., focal distance, focus, frame rate, ISO, sensortemperature, shutter speed, aperture, etc.).

I/O interface 170 is a device that allows a user to send action requeststo console 150. An action request is a request to perform a particularaction. For example, an action request may be to start or end anapplication or to perform a particular action within the application.I/O interface 170 may include one or more input devices. Example inputdevices include a keyboard, a mouse, a game controller, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 150. An action request received byI/O interface 170 is communicated to console 150, which performs anaction corresponding to the action request. In some embodiments, I/Ointerface 170 may provide haptic feedback to the user in accordance withinstructions received from console 150. For example, haptic feedback isprovided by the I/O interface 170 when an action request is received, orconsole 150 communicates instructions to I/O interface 170 causing I/Ointerface 170 to generate haptic feedback when console 150 performs anaction.

Console 150 provides content to HMD 101 for presentation to the user inaccordance with information received from imaging device 160, HMD 101,or I/O interface 170. In the example shown in FIG. 1 , console 150includes application store 152, tracking module 154, and engine 156.Some embodiments of console 150 have different or additional modulesthan those described in conjunction with FIG. 1 . Similarly, thefunctions further described below may be distributed among components ofconsole 150 in a different manner than is described here.

Application store 152 stores one or more applications for execution byconsole 150. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of HMD 101 or interface device 170.Examples of applications include gaming applications, conferencingapplications, video playback application, or other suitableapplications.

Tracking module 154 calibrates system 100 using one or more calibrationparameters and may adjust one or more calibration parameters to reduceerror in determining position of HMD 101. For example, tracking module154 adjusts the focus of imaging device 160 to obtain a more accurateposition for observed locators 114 on HMD 101. Moreover, calibrationperformed by tracking module 154 also accounts for information receivedfrom IMU 116. Additionally, if tracking of HMD 101 is lost (e.g.,imaging device 160 loses line of sight of at least a threshold number oflocators 114), tracking module 154 re-calibrates some or all of thesystem components.

Additionally, tracking module 154 tracks the movement of HMD 101 usingslow calibration information from imaging device 160 and determinespositions of a reference point on HMD 101 using observed locators fromthe slow calibration information and a model of HMD 101. Tracking module154 also determines positions of the reference point on HMD 101 usingposition information from the fast calibration information from IMU 116on HMD 101. Additionally, tracking module 154 may use portions of thefast calibration information, the slow calibration information, or somecombination thereof, to predict a future location of HMD 101, which isprovided to engine 156.

Engine 156 executes applications within the system and receives positioninformation, acceleration information, velocity information, predictedfuture positions, or some combination thereof for HMD 101 from trackingmodule 154. Based on the received information, engine 156 determinescontent to provide to HMD 101 for presentation to the user, such as avirtual scene. For example, if the received information indicates thatthe user has looked to the left, engine 156 generates content for HMD101 that mirrors or tracks the user's movement in a virtual environment.Additionally, engine 156 performs an action within an applicationexecuting on console 150 in response to an action request received fromthe I/O interface 170 and provides feedback to the user that the actionwas performed. The provided feedback may be visual or audible feedbackvia HMD 101 or haptic feedback via I/O interface 170.

FIG. 2 is a diagram of HMD 101, in accordance with at least oneembodiment. In this example, HMD 101 includes a front rigid body and aband that goes around a user's head. The front rigid body includes oneor more electronic display elements corresponding to electronic display102, IMU 116, head tracking sensors 118, and locators 114. In thisexample, head tracking sensors 118 are located within IMU 116. Note inembodiments, where the HMD 101 is used in AR and/or MR applicationsportions of the HMD 101 may be at least partially transparent (e.g., aninternal electronic display, one or more sides of the HMD 101, etc.).

Locators 114 are located in fixed positions on the front rigid bodyrelative to one another and relative to reference point 200. In thisexample, reference point 200 is located at the center of IMU 116. Eachof locators 114 emits light that is detectable by imaging device 160.Locators 114, or portions of locators 114, are located on a front side,a top side, a bottom side, a right side, and a left side of the frontrigid body, as shown FIG. 2 .

Focus Adjustment Method

As discussed above, varifocal system 100 may dynamically vary the focusdepth to bring images presented to a user wearing HMD 101 into focus,which keeps the user's eyes in a zone of comfort as vergence andaccommodation change. Additionally, eye tracking in combination with thevariable focus of the varifocal system allows blurring to be introducedas depth cues in images presented by HMD 101.

Accordingly, a position, orientation, and/or a movement of HMD 101 isdetermined by a combination of locators 114, IMU 116, head trackingsensors 118, imagining device 160, and tracking module 154, as describedabove in conjunction with FIG. 1 . Portions of a virtual scene presentedby HMD 101 are mapped to various positions and orientations of HMD 101.Thus, a portion of the virtual scene currently viewed by a user isdetermined based on the position, orientation, and movement of HMD 101.After determining the portion of the virtual scene being viewed by theuser, the system may then determine a location or an object within thedetermined portion at which the user is looking to adjust focus for thatlocation or object accordingly.

To determine the location or object within the determined portion of thevirtual scene at which the user is looking, HMD 101 tracks the positionand location of the user's eyes. Thus, HMD 101 determines an eyeposition for each eye of the user. For example, HMD 101 tracks at leasta subset of the 3D position, roll, pitch, and yaw of each eye and usesthese quantities to estimate a 3D gaze point of each eye. Further,information from past eye positions, information describing a positionof the user's head, and information describing a scene presented to theuser may also be used to estimate the 3D gaze point of an eye in variousembodiments. For example, FIG. 3 shows a cross section of an embodimentof HMD 101 that includes camera 302 for tracking the position of eacheye 300. In this example, camera 302 captures images of the user's eyesand eye tracking module 110 determines an output for each eye 300 andgaze lines 304 corresponding to the gaze point or location where theuser is looking based on the captured images.

A Vergence depth (d_(v)) 308 of the gaze point for the user isdetermined based on an estimated intersection of gaze lines 304. Asshown in FIG. 3 , gaze lines 304 converge or intersect at d_(v) 308,where object 306 is located. Because virtual distances within thevirtual scene are known to the system, the vergence depth 308 can befiltered or verified to determine a more accurate vergence depth for thevirtual scene. For example, vergence depth 308 is an approximation ofthe intersection of gaze lines 304, which are themselves anapproximation based on the position of a user's eyes 300. Gaze lines 304do not always appear to accurately intersect. Thus, in one embodiment,virtual distances within the virtual scene can be compared to thevergence depth for the portion of the virtual scene to generate afiltered vergence depth.

Determining a more accurate vergence depth or gaze point enables thevirtual scene to more accurately determine a user's object or plane offocus, allowing scene rendering module 120 to add depth of field blur toproper depths and/or objects in the virtual scene or otherwise modify tovirtual scene to appear more realistic. Further, if virtual sceneincludes multiple objects, the vergence processing module 112 maycompare the estimated vergence depth to distances associated with atleast a subset of the objects. In one example, the minimum differencebetween distance to an object and the estimated vergence depth isdetermined to be the filtered vergence depth; however, other methods ofidentifying an object that specifies the filtered vergence depth may beused in various embodiments.

A state of optics block 104 is determined for a frame of the virtualscene based on states of optics block 140 during presentation ofprevious frames of the virtual scene. For example, focus predictionmodule 108 tracks the state of optics block 104 for various frames ofthe virtual scene to predict to future a state of optics block 104 forsubsequent frames of the virtual scene. The predicted state of opticsblock 104 (e.g., a predicted location of optics block 104) allows thescene rendering module 114 to determine an adjustment to apply to aframe of the virtual scene so distortion caused by the predicted stateof optics block 104 corrects or cancels the applied adjustment ratherthan distorting the frame. Thus, based on the state of optics block 104,a distortion correction is determined for application to a frame of thevirtual scene to correct optical error introduced by the state of opticsblock 104.

Accordingly, the focal distance is adjusted for the presented frame ofthe virtual scene to provide accommodation for the generated filteredvergence depth by moving one of electronic display 102 or optics block104. FIGS. 4A and 4B show an example process for adjusting the focaldistance by changing the distance between electronic display 102 andoptics block 104 using varifocal actuation block 106. In the example ofFIGS. 4A and 4B, varifocal actuation block 106 includes an actuator,motor, track, and so forth that will be further described with respectto FIGS. 5A-21B that allow electronic display 102, optics block 104, orboth to move relative to each other to dynamically adjust the adjust thefocal distance d.

FIG. 4A shows an example of HMD 101 providing focus adjustment for framen of a scene. In this example, the scene includes object 400 displayedon electronic display 102 at which the gaze of user 402 is directed(i.e., verged). A virtual image of object 400 is located a virtualdistance d_(i), behind electronic display 102, from exit pupil 404. Inthe example of FIG. 4A, electronic display 102 is in position pi, whichprovides accommodation for distance d_(i) to enable comfortable viewingof object 400.

FIG. 4B shows HMD 101 providing s focus adjustment for a subsequentframe n+1 of the virtual scene. In this example, user 402 may haverepositioned its eyes to look at object 406 or object 406 quickly movedtoward user 402 in the scene. As a result, the virtual image of object406 is located close to electronic display 102. In response to thelocation of object 406 close to the electronic display 102, which iscloser than object 400 in FIG. 4A), eyes of user 402 rotate inward toverge on object 406, causing vergence processing module 112 to determinea new vergence depth for frame n+1 and to provide the new vergence depthto varifocal actuation block 106. Based on the new vergence depth,varifocal actuation block 106 moves electronic display 102 from positionpi to new position pf to accommodate user 402 at the new vergence depthd_(f) for the closer object 406.

In one example, each state of optics block 104 corresponds to acombination of focal distance and eye position, provides accommodationfor a range of vergence depths, and is associated with a specificposition of optics block 104. Accordingly, vergence depths may be mappedto positions of optics block 104 and stored in a lookup table. Thus,when a vergence depth is received from vergence processing module 112,varifocal actuation block 106 automatically moves optics block 104 to aposition corresponding to the received vergence depth based on thelookup table.

In many instances, virtual reality systems aim to present users with avirtual environment that closely simulates a real world environment orprovides users with content causing the users to get lost in theillusion created by the virtual reality systems. To provide users with arealistic or captivating virtual environment, a virtual reality systemimplements multiple systems and methods discussed herein to operatetogether at efficiencies that are imperceptible to a user. For example,transition delays are particularly costly to user experience withvirtual reality systems. If a user is waiting for the virtual scenepresented by a HMD to catch up to what the user's brain is alreadyexpecting, the illusion is broken and/or the user may get nauseous.However, processing speeds and commercially available actuators arecurrently faster than the coordination of the human eye to change theshape of its lens and the human brain to register what the new shape ofthe lens is focused on, allowing the disclosed systems and methods toprovide users with high-quality virtual environments.

The frame of the virtual scene corresponding to the portion of thevirtual scene being viewed by the user is displayed on electronicdisplay 102 with a distortion correction to correct optical error causedby the determined state of optics block 104 and with depth of field blurbased on the vergence depth. Further, varifocal actuation block 106 haschanged the focus of optics block 104 to provide focus and accommodationto the location in the portion of the virtual scene where the user'seyes are verged.

Display of a scene by HMD 101 is modified to mitigate distortionintroduced by optical errors of optics block 104 included in HMD 101that directs image light from electronic display element 102 presentingthe scene to an eye of a user. A distortion correction is applied to thescene that pre-distorts the scene, and distortion caused by optics block140 compensates for the pre-distortion as light from the modified scenepasses through optics block 104. Hence, the scene viewed by the user isnot distorted. Accordingly, distortion corrections account for differentlevels and types of distortion caused by different eye positionsrelative to optics block 104 or different focal distances of HMD 101.Accordingly, the distortion corresponding to different potential eyepositions relative to optics block 104 and at potential focal distancesfor HMD 101 is determined by measuring a wavefront (i.e., propagation ofpoints of the same phase) of light from the electronic display elementafter the light has passed through the optics block. Different eyepositions relative to optics block 104 and different states of opticsblock 104 cause different degrees of optical error in light directedthrough optics block 104. This optical error distorts light fromelectronic display element 102 included in HMD 101, which may impairpresentation of a virtual scene to a user. Accordingly, distortioncorrection maps are generated based on measurements of the wavefront fordifferent states of optics block 104 to correct for optical errorintroduced by the different states of optics block 104, which accountsfor different focal distances of HMD 101.

Varifocal Actuation

As described above, varifocal actuation block 106 enables dynamicadjustment of the focal distance of HMD 101 to keep a user's eyes in azone of comfort as vergence and accommodation change. In one embodiment,varifocal actuation block 106 physically changes the distance betweenelectronic display 102 and optical block 104 by moving electronicdisplay 102 or optical block 104 (or both). Moving or translating twolenses that are part of optical block 104 relative to each other mayalso be used to change the focal distance of optics block 104 of HMD 101to change the focal distance.

FIGS. 5A-5C show one implementation of varifocal actuation block 106 fora portion of one embodiment of HMD 101 corresponding to a single eye ofa user that includes electronic display 102, optical block 104, andvarifocal actuation block 106. Thus, as shown, HMD 101 would include twosuch portions of HMD 101 that would include two electronic displays 102,optical blocks 104, and varifocal actuation blocks 106; however, inother embodiments, HMD 101 may include a single electronic display 102and a single varifocal actuation block 106. Additionally, otherconfigurations of components described herein are possible.

FIG. 5A is a perspective view of a portion of HMD 101 that includeselectronic display 102, optical block 104, and varifocal actuation block106. Varifocal actuation block 106, in one embodiment, includesactuating motor 502 (e.g., DC brushed or brushless motor, stepper motor,etc.) and drive mechanism 504 (e.g., power screw, ball screw, gearedspindle drive, etc.) fixed relative to optical block 104 (e.g., mounteddirectly to optics block 104, a housing of HMD 101, or a secondarybracket of HMD 101 etc.) to move electronic display 102 toward and awayfrom optics block 104 along optical axis 550 (or z-axis) of via one ormore guides 506.

FIG. 5B is a top view of the portion of HMD 101 shown in FIG. 5A thatadditionally shows camera 502 and hot mirror 552, in one embodiment ofHMD 101. As described above, the position of electronic display 102, inthis embodiment, is driven by (or adjusted in response to) the plane offocus corresponding to a vergence depth determined from the vergenceangle of the user's eyes, as a function of real-time eye tracking. Theposition of each eye is captured by camera 302 which is located off-axis(i.e., at an angle relative to optical axis 550), in one embodiment. Inthis embodiment, camera 302 is an infrared (IR) camera that receives IRlight reflected from the eye of the user via hot mirror 552 locatedbetween electronic display 102 and optics block 104. Hot mirror 552 ispositioned at an angle relative to electronic display 102 in order toreflect the IR light off-axis toward camera 302. Here, hot mirror 552 istransparent to visible light to allow the visible light from electronicdisplay 102 to pass through to a viewing user unimpeded while reflectingthe IR light to camera 302. Thus, camera 302 captures IR light reflectedfrom a retina of the user (and hot mirror 552) and this information forthe position of the user's eye is provided to determine the vergencedepth.

Accordingly, the focal distance of HMD 101 is adjusted to match thedetermined vergence depth. Drive mechanism 504, in substantiallyreal-time, moves electronic display 102 relative to optics block 104 tofocus HMD 101 to the determined vergence depth utilizing screenpositioning feedback via linear or proximity encoder 508. In thisimplementation, a positional precision of ˜100 microns or better isideal and achievable with commercially available linear encodingsystems.

FIG. 5C shows a blow-up view of the portion of HMD 101 described withrespect to FIGS. 5A-5B. Here, components of electronic display 102,optical block 104, and varifocal actuation block 106 are shownseparately with indications corresponding to how each of electronicdisplay 102, optical block 104, and varifocal actuation block 106 fittogether. Accordingly, drive mechanism 504 of varifocal actuation block106 includes power screw 510 driven by motor 502 and nut-sled 512. Powerscrew 510 and motor 502 are supported by bracket 520, which can be fixedto a housing of HMD 101 or to optics block 104. Although shown outsideof bracket 520, motor 502 could be located parallel to power screw 510inside of bracket 520 and engage power screw 510 through gears locatedoutside of bracket 520 (e.g., a first gear for motor 502 and a secondgear for power screw 510). Nut-sled 512 includes push pin 514 and isthreaded to move along power screw 510 when power screw 510 is turnedand moves back and forth depending on which direction power screw 510 isturned. Additionally, a spring could be located between power screw 510and bracket 520 or a spring with an integrated anti-backlash nut. Drivemechanism 504 may also use different screw types including a nut-sledinteraction and screw end support methodologies.

In this implementation, optics block 104 is fixed within HMD 101 andelectronic display 102 is moved relative to optics block 104 based onthe determined vergence depth. Here, electronic display 102 is mountedto display bracket 516 that includes display bracket arm 518 and guidepins 520. Accordingly, display bracket arm 518 receives or engages pushpin 514 of drive mechanism 504 and guide pins 520 slide freely withinguides 506. Thus, as nut-sled 512 moves along power screw 510, push pin514 engages display bracket arm 518 and moves display bracket 516 thatsupports electronic display 102, and guide pins 520 guide the movementof electronic display 102 relative to optics block by engaging guides506 of optics block.

FIGS. 6A-6B shows another implementation of varifocal actuation block106 for a portion of one embodiment of HMD 101 that uses cam and rollerdrive mechanism. FIG. 6A is a perspective view and FIG. 6B is a top viewof a portion of HMD 101 that includes electronic display 102, opticalblock 104, and varifocal actuation block 106. Varifocal actuation block106, in this embodiment, similarly includes actuating motor 502 (e.g.,DC brushed or brushless motor, stepper motor, etc.) and drive mechanismthat includes cam 602 connected to actuating motor 502 and roller 604connected to display bracket 516 that engages cam 602 that moveelectronic display 102 toward and away from optics block 104 via one ormore guides 506. In this implementation, the radius of cam 602 is notconstant (e.g., an eccentric cam) and, as motor 502 turns cam 602, thechanging radius of cam 602 moves electronic display 102 closer orfarther away from optics block 104 depending on the direction cam 602 isturned.

Although shown positioned horizontally, cam 602 and roller 604 mayalternatively be positioned vertically. Cam 602 and roller 604 mayengage each other via gears or by sliding contact. Display bracket 516may additionally be biased toward optics block 104 via one or moresprings either between display bracket 516 and the housing of HMD 101 oralong guide pins that engage guides 506. In another embodiment, roller604 may not be necessary. For example, cam 602 could be an eccentric camwith a changing radius that directly engages an arm or extension ofdisplay bracket 516, such as in a sliding manner or via gear teeth.Thus, as cam 602 turns, the change in thickness of the radius of cam 602sliding against display bracket 516 causes display bracket 516 to moveeither closer to or farther away from optics block 104 depending onwhich direction cam 602 is turned. In such an implementation, cam 602may include a sliding perimeter bushing or bearing that may minimizefriction against display bracket 516.

FIG. 7 show another implementation of varifocal actuation block 106 thatuses a face cam 702 of varying thickness that pushes against pushcontact roller 704 to move electronic display 102. Accordingly, motor502 (e.g., DC brushed or brushless motor, stepper motor, etc.) isconnected to first gear 706 that engages second gear 708 that isconnected to face cam 702. Thus, in this implementation, electronicdisplay 102 is biased away from optics block 104 via one or more springs710 and, as motor 502 turns first gear 706, first gear 706 turns secondgear 708, thereby turning face cam 702. As face cam 702 is turned, pushcontact roller 704 is pressed toward (or away from) optics block 104based on the varying thickness of face cam 702 to move electronicdisplay 102 relative to optics block 104. Other cam implementations areadditionally achievable. For example, a cam and dual roller, a trappedEccentric Cam inside of a larger cylindrical feature or whole created aspart of display bracket 516, and pin in a spiral cam groove, a negativecut cam, and so forth.

FIG. 8 shows another implementation of varifocal actuation block 106that uses pivoting arm 802 to move display bracket 516 that supportselectronic display 102. Accordingly, pivoting arm 802 that includes apin engages drive slot 804 of display bracket 516 that supportselectronic display 102. In this implementation, display bracket includesa top pivot arm 802 and a bottom pivot arm (not shown) supportingelectronic display 102 between each pivot arm. In one embodiment, motor502 includes a gear head that is provided off-axis, as shown in FIG. 8 ,but also includes a custom gear train through a shaft, for example, thatlinks both pivoting arms for symmetric force application and movement ofelectronic display 102 in the z-direction.

FIGS. 9A-9C show implementations of varifocal actuation block 106 usinga gear and rack. FIG. 9A utilizes rolling or sliding contact surfaces toinduce translation of electronic display 102 in the z-direction andshows gear 902 driven by motor 502 which engages rack 904, which variesin thickness. In this implementation, the thickness of rack 904increases with distance away from an end of rack 1304 that includesteeth that engage gear 1302. Here, display bracket 516 supportingelectronic display 102 is biased away from optics block 104 via aspring. Thus, the thickest part of rack 904 would push display bracket516 closer to optics block 104 relative to a least thick part of rack904. Accordingly, in operation, motor 902 turns gear 902 which engagesrack 904 to thereby move display bracket 516 forward or backwarddepending on a starting and stopping thickness of rack 904 exerting aforce on display bracket 516. Thus, the varifocal actuation block 106,shown in FIG. 9A, is essentially a linear CAM, or sometimes referred toas a Wedge.

FIGS. 9B and 9C show other implementations of varifocal actuation block106 using a gear and rack. In these implementations, the rackcorresponds to arm 906 of display bracket 516 that is perpendicular toelectronic display 102. FIG. 9B shows motor 902 directly connected togear 902 that engages arm 906 (e.g., rack and pinion) to move electronicdisplay 102. FIG. 9C shows worm gear 908 engaging gear 902 that engagesarm 906 (e.g., rack and pinion with worm gear) to move electronicdisplay 102.

Other implementations of varifocal actuation block 106 using a gear andrack are achievable. For example, in one implementation, the rack couldbe provided teeth upward and attached to display bracket 516. To offseta motor driven worm gear, a smaller spur gear that engages the teeth ofthe rack is attached to a worm spur gear of a larger radius forsynchronous rotation. Thus, as the worm gear is turned by the motor, theworm gear turns the worm spur gear that synchronously turns the spurgear with a smaller radius, and the smaller spur engages the rack teeth,thereby, causing electronic display 102 to move either toward or awayfrom optics block 104 depending on the direction of rotation of the wormgear. Moreover, worm gear 908, instead of engaging gear 902, coulddirectly engage arm 906 to move electronic display 102.

FIGS. 10A-10D show implementations of varifocal actuation block 106using a cable or belt drive and one or more pulleys. FIG. 10A showsvarifocal actuation block 106 as a windup pulley actuator that includesfirst pulley 1002 connected to motor 502 (e.g., DC brushed or brushlessmotor, stepper motor, etc.), cable 1004, and idle tension pulley 1006.In this implementation, electronic display 102 is biased away fromoptics block 104 via one or more springs and first pulley 1002 pullselectronic display 102 toward optics block 104 via cable 1004 which isanchored to display bracket 516 supporting electronic display 102.

Alternatively, electronic display 102 is biased toward optics block 104via one or more springs 1008 mounted to the housing of HMD 101, forexample, and pulley 1002 pulls electric display 102 away optics block104 via cable 1004, as shown in FIG. 10B. In this implementation, cable1004 is anchored to display bracket 516 supporting electronic display102 from behind and wrapped around via two idle tension pulleys 1006.Thus, motor 502 turns first pulley 1002 in one direction to compresssprings 1008 and thereby moving electronic display away from opticsblock 104 and releases tension in springs 1008 by turning first pulley1002 in the opposite direction. Using multiple idle tension pulleys1006, first pulley 1002 can be located in many different locations.

FIG. 10C shows varifocal actuation block 106 as a belt drive actuatorthat includes first pulley 1002 connected to motor 502 and belt 1010around first pulley 1002 and idle pulley 1006. In this implementation,bracket 1012 is fixed to belt 1010 and to arm 1014 of display bracket516. Thus, as motor 502 turns first pulley 1002, belt 1010 moveselectronic display 102 toward or away from optics block 104.

Further, FIG. 10D shows a friction drive wheel implementation ofvarifocal actuation block 106. In this example, friction drive plate1016 is connected to arm 1014 of display bracket 516 and sandwichedbetween contact drive wheel 1018 and secondary support wheel 1020.Contact drive wheel 1018 is driven by motor 502 and frictionally engagesfriction drive plate 1016. Thus, as motor 502 turns contact drive wheel1018, friction drive plate 1016 is driven back and forth in thez-direction to move electronic display 102 toward or away from opticsblock 104.

FIG. 11 shows another implementation of varifocal actuation block 106where electronic display 102 is attached to threaded ring 1102 thatengages a threaded portion of an end of optics block 104. Accordingly,threaded ring 1102 and electronic display 102 moves telescopically inthe z-direction when threaded ring 1102 is turned via motor 502 and spurgear 1106. In this implementation, electronic display 102 is biasedtoward optics block 104 via springs 1104 and is pushed away from opticsblock 104 as motor 502 turns spur gear 1106.

FIG. 12 shows an implementation of varifocal actuation block 106 where agear threaded actuator is attached to a center of electronic display 102pushes electronic display 102 from behind. Accordingly, electronicdisplay 102 is attached to threaded post 1202 from behind. Exterior gear1204 includes teeth on the exterior and is internally threaded to engagethreaded post 1202. Spur gear 1206 is attached and turned by motor 502and engages exterior gear 1604. Thus, as motor 502 turns spur gear 1206,spur gear 1206 turns exterior gear 1204 causing threaded post 1202 tomove electronic display 102 back and forth relative to optics block 104via the threaded engagement between threaded post 1202 and exterior gear1204 depending on which direction motor 502 turns spur gear 1206.Alternatively, motor 502 could be mounted directly behind electronicdisplay 102 with the threaded “nut” feature attached to the screenbracket, and the motor shaft rotating the threaded power screw to pushit back and forth.

FIGS. 13A-13C show various implementations of varifocal actuation block106 using a solenoid or Voice Coil Actuator (VCA) as a motor to drivemovement of electronic display 102. FIG. 13A is a perspective view of animplementation that includes multiple varifocal actuation blocks 106that each include voice coil 1304, guide 1306, and spring 1308integrated together on each guide pin 1302 guiding or confining thedirection of travel of electronic display 102 relative to optics block104. Accordingly, in this implementation, guide pins 1302 are shown thateach include a voice coil 1304 and spring 1308 and engage a guide 1306of optics block 104 for movement in the z-direction.

In one embodiment, voice coil 1304 is a ferrite guide positioned betweendisplay bracket 516 supporting electronic display 102 and optics block104. In this implementation, spring 1308 biases electronic screen 102away from optics block 104 and, when actuated by allowing current toflow through the coil of voice coil 1304, the electromagnetic fieldcreated by the coil of voice coil 1304 attracts an iron core of voicecoil 1304, causing spring 1308 to compress, and thereby movingelectronic display 102 closer to optics block 104. When the coil isde-energized, the force applied by spring 1308 pushes the iron corevoice coil 1304 back toward its original position, thereby movingelectronic display 102 back away from optics block 104. The more currentflowing through the coil of voice coil 1304, the stronger theelectromagnetic field, the more each spring 1308 is compressed, and thecloser electronic display 102 moves toward optics block 104.Accordingly, the more spring 1304 is compressed, the closer electronicdisplay 102 is to optics block 104 in this implementation.

Although shown in FIG. 13A as multiple varifocal actuation blocks 106, asingle varifocal actuation block 106 off-axis could alternatively beimplemented. Additionally, a single varifocal actuation block 106on-axis positioned in the center on a back side of electronic display102 could be implemented. FIG. 13B shows voice coil 1304 mounted on theback of electronic display 102, in one embodiment. In thisimplementation, voice coil 1304 is back-mounted on the center ofelectronic display 102 on one end and to a housing of HMD 101 or otherstationary bracket. Thus, when actuated by allowing current to flowthrough the coil of voice coil 1304, electronic display 102 moves closerto optics block 104 and, when de-energized, spring 1308 pusheselectronic display 102 back away from optics block 104.

FIG. 13C shows a voice coil implementation, in one embodiment, ofvarifocal actuation blocks 106. In this implementation, voice coil 1310is mounted on the back-center of electronic display 102 and includesmagnet 1312. The other end voice coil 1310 is mounted or attached to ahousing of HMD 101 or other stationary bracket. Accordingly, driving acurrent through voice coil 1310 produces a magnetic field that causesvoice coil 1310 to move relative magnet 1312, thereby moving electronicdisplay 102.

FIG. 14 shows an implementation of varifocal actuation block 106 thatuses a linear motor. In one embodiment, the linear motor is analternating north-south poled shaft with solenoid style driving coil. Inthis implementation, north-south poled shaft 1402 is attached to opticsblock 104 via bracket 1406 and drive coil 1404 that moves alongnorth-south poled shaft 1402 is attached to display bracket 516.Accordingly, as a current is applied to drive coil 1404, drive coil willmove along north-south poled shaft 1402 and, since electronic display102 is attached to display bracket 516, the applied current moveselectronic display 102 relative to optics block 104. Although shownattached to optics block 104 via bracket 1406, north-south poled shaft1802 could alternatively be mounted to a housing of HMD 101 or someother bracket that is fixed relative to optics block 104. Thus, as drivecoil 1804 moves along north-south poled shaft 1402, electronic display102 will move relative to optics block 104 in a similar manner. Inanother embodiment, the linear motor could be a Linear Tube Servo, amongother possibilities.

FIG. 15A shows an implementation of varifocal actuation block 106 thatuses Piezo bending to move electronic display 102, in one embodiment.Piezo walking linear stages utilize rapid expansion and contractioncharacteristics of piezo element with applied voltage, to “walk” shaftin and out. Piezo bend use thin Piezo layers on a pre-loaded substrateto act as a return spring. In this implementation, FIG. 15A showsdisplay bracket 516 that supports electronic display 102 movablerelative optics block 104 via guide pins 520 of display bracket 516 andguides 506 of optics block 104. Display bracket 516 (and electronicdisplay 102) is biased toward optics block 104 via springs 1504.Accordingly, Piezo layered substrate 1902 is located between electronicdisplay 102 and optics block 104 to push electronic display 102 awayfrom optics block 104 when a voltage is applied.

Although shown with springs 1504 anchored to a housing of HMD 101 orother bracket and Piezo layered substrate 1502 located betweenelectronic display 102 and optics block 104, springs 1504 couldalternatively be located between electronic display 102 and optics block104 and Piezo layered substrate 1502 could be anchored to the housing ofHMD 101 or other bracket and Piezo layered substrate 1502. Further,various implementations could make use of multiple Piezo layers stackedto amplify motion.

FIGS. 15B-15C show example pneumatic or hydraulic actuationimplantations of varifocal actuation block 106 that uses a gas or liquidpressure to move one or more pistons or a diaphragm to move electronicdisplay 102 relative to optics block 104. FIG. 15B shows piston 1506 andvalve stem 1508 with valve stem 1508 attached to an arm of displaybracket 516. Thus, as pressure forces valve stem 1508 of piston 1506 tomove in the z-direction, electronic display 102 is moved away fromoptics block 104. Further, although not shown, electronic display 102could be spring biased away from optics block 104. Alternatively, theactuator of FIG. 15B including piston 1506 and valve stem 1508 could bereplaced with a Piezo linear motor, a Piezo Linear Ultrasonic drive, aPiezo inertia drive (e.g., stick slip drive), a Piezo Bender (e.g., aPiezo Bimorph), or a Piezo Strain Amplifier (Piezo Flexure Drive) tomove electronic display 102 in the z-direction.

FIG. 15C shows diaphragm pneumatic or hydraulic actuator 1506 thatincludes diaphragm 1510. In this example, electronic display 102 isspring biased away from optics block 104 via springs 1512 and diaphragm1510, when pressure is forced into diaphragm 1510, provides the motivepower to move electronic display 102 against spring 1512 toward opticsblock 104.

Interpupillary Distance Adjustment

FIGS. 16A-16D show various implementations of varifocal actuation block106 that allow for interpupillary distance (IPD) adjustment. Here, FIGS.16A-16D are directed to implementations of the contact between varifocalactuation block 106 and display bracket 516 to allow the actuationsystem to be mounted fixed, to the housing, while permitting electronicdisplay 102 and optics block 104 to translate on IPD rails.

FIG. 16A shows an arm extension of display bracket 516 that allowsrolling CAM or eccentric roller 1602 to push against display bracket 516and thereby move electronic display 102 that is spring biased towardoptics block 104. The arm extension of bracket display 516 allows for alarger or longer section of contact for roller 1602 to allow electronicdisplay 102 and optics block 104 to move laterally (x-direction)relative to varifocal actuation block 106, thereby allowing a user toadjust the interpupillary distance of HMD 101 to fit their face.

Similarly, FIG. 16B shows another implementation including screwadjustable or spring biased contact back plate 1604 that engages roller1602. FIG. 16B also includes an arm extension of display bracket 16allows for a larger or longer section of contact for roller 1602 toallow lateral (x-direction) movement of electronic display 102 andoptics block 104 relative to varifocal actuation block 106. In thisexample, however, electronic display 102 is not spring biased towardoptics block 104 and nut-sled 512 is secured via roller 1602 (thatallows the lateral adjustment) to display bracket 516 by adjustablecontact back plate 1604.

FIG. 16C-16D include push-pin 514 that attaches to bracket arm 518 ofdisplay bracket 516 that supports electronic display 102. Accordingly,FIG. 16C shows push-pin 514 provided horizontally (protruding in thex-direction) and capable of sliding back and forth within a holeprovided for push-pin 514 in bracket arm 518 of display bracket 516.Push-pin 514 is provided at a length that allows push-pin 514 to engagebracket arm 518 at various lengths to allow electronic display 102 andoptics block 104 to move laterally (x-direction) relative to varifocalactuation block 106, thereby allowing a user to adjust theinterpupillary distance of HMD 101.

Similarly, FIG. 16D shows an implementation of varifocal actuation block106 that includes push-pin 514 provided vertically (i.e., y-direction)via an extension of nut-sled 512. Push-pin 514, in this example, engagesbracket arm 518 of display bracket 516 via slot 1606. Slot 1606 iselongated in the x-direction to allow lateral adjusts of electronicdisplay 102 and optics block 104 relative to varifocal actuation block106 by moving push-pin 514 back and forth (in the x-direction) withinslot 1606 to similarly change the interpupillary distance.

Accordingly, the implementations of varifocal actuation block 106 shownFIGS. 16A-16D allow for interpupillary distance (IPD) adjustment whilemotor 502 is mounted to the housing of HMD 101. In other embodiments,motor 502 is mounted to the optics block 104, directly or via asecondary bracket. In this embodiment, motor 502 moves with optics block104 as the IPD is adjusted.

Varifocal Guidance

FIG. 17A shows an example of flexure based guidance system using one ormore flexures 1702. A Flexure based guidance system makes use ofmechanical stress applied to a flexure that causes the flexure to moveor change shape. Flexure based guidance is friction-free when comparedto shaft/pin in bushing guidance, can potentially be implemented withfewer/cheaper parts, and may be integrated to molded plastic parts.Flexures 1702, as shown in FIG. 17A, add a linear spring force that canmove electronic display 102 and could be designed to permit fairlystrict single degree of freedom motion. For example, FIG. 17A showsflexure 1702 as a less strict leaf spring embodiment that may rely onthe actuation system design to minimize tip-tilt and off axis slide.

FIGS. 17B and 17C show a side cut view and a perspective view,respectively, of varifocal actuation block 106 using a flexure guidancesystem. In this example, varifocal actuation block 106 includes a dualflexure guidance assembly with a first flexure 1702 a, a second flexure1702 b, and actuator 1704 (e.g., a motor, a voice coil, etc.) connectedto the back of electronic display 102. A bracket 1706 supportselectronic display 102 (i.e., electronic display 102 is mounted tobracket 1706), actuator 1704, in this example, is mounted behindelectronic display 102 in the center of bracket 1706, and first flexure1702 a and second flexure 1702 b guide or constrain movement of bracket1706 (and, therefore, electronic display 102) in the directionperpendicular to the plane of electronic display 102.

In a rested state absent of any applied force, first flexure 1702 a andsecond flexure 1702 b are planar. FIG. 17D shows flexure 1702 a (or 1702b) by itself, in one embodiment, and FIG. 17E shows a perspective viewof varifocal actuation block 106 with the dual flexure guidance assemblythat includes first flexure 1702 a and second flexure 1702 b inoperation as actuator 1704 moves electronic display 102. Flexures 1702 aand 1702 b can be made from stainless steel, titanium, aluminum, acomposite material, a plastic, an elastomer, and so forth and are planaror flat at rest, but are patterned (by etching, carving, etc.), as shownin the example of FIG. 17D, to guide movement in the z-direction.

In one embodiment, the pattern is designed to encourage or merely allowmovement in the z-direction while resisting movement in the x ory-direction. In one embodiment, the pattern first flexure 1702 a andsecond flexure 1702 b operates a spring bias toward an equilibrium wheneach flexure is flat. The flexure(s) could also be married to actuator1704 via the use of a “nut” and power screw to create a rotary styleactuator. In another embodiment, the dual flexure guidance assembly thatincludes first flexure 1702 a and second flexure 1702 b could beprovided with actuator 1704 located off to the side, as described andshown with respect to FIGS. 5A-5C.

FIG. 18 shows an example guidance method using Pin, Shaft, or shaft inbushings, linear bearings, or features. Combinations of a full radiusbushing, and a C-shaped half bushing 506 b may be used to not“over-constrain” a guidance system consisting of at least one guide pin520 and guide 506 a and C-shaped half bushing 506 b of optics block 104.Here, guide pin 520 is fixed to (or apart of) screen bracket 516 andguide 506 a and C-shaped half bushing 506 b of optics block 104constrain or guide motion of electronic display 102 via guide pin(s) 520to allow movement in the z-direction. Other guiding features or methodsmay also be integrated into screen bracket 516, the housing of HMD 101,or optics block 104 directly. This guidance method could be used, forexample, in conjunction with FIGS. 5A-6B. C-shaped half bushing 506 b isonly one of many possibilities that could be used in this category. Forexample, C-shaped half bushing 506 b could be replaced with two fullradius bushings, a full radius bushing and a v-slot bushing, two v-slotbushings, and forced bias applied via spring, screw, magnet, or flexureto any of the above configurations to one or both bushings, or one orboth guide rods.

There are, in one embodiment, two guide pins 520 a and 520 b, one guide506 a, and one C-shaped half bushing 506 b that the guide pins 520 fitinto. One of the guide pins 520 is referred to as the Primary Guide(i.e., the guide pin that fits into guide 506 a) because it does most ofthe guidance work including controlling the motion in all the degrees offreedom except for rotation, and the remaining axis of desired travel.The Primary Guide usually goes into one long bushing (e.g., guide 506a), or two separated along its axis to increase the span like a longbushing (same effect).

The other guide may be referred to as the Secondary Guide (e.g., guidepin 520), which only prevents the moving element from rotating aroundthe Primary Guide. The C-shaped half bushing 506 b for the primary guidecan be shorter relative to guide 506 a, and since it only controlsrotation, the “Open-C” shape is best. Accordingly, in one embodiment,power screw 510 (leadscrew) itself could operate as the Primary Guide,thereby, obviating the need for guide pin 520 a and guide 506 a. Thus,nut-sled 512 acts as the Bushing, using the exterior surface of powerscrew 510 as its Primary Guide Rod and the secondary guide is the sameC-shaped half bushing 506 b.

Further, in one embodiment, the guide pins 520 a and 520 b could bemounted statically to optics block 104 and the guide 506 a and C-shapedhalf bushing 506 b could be mounted on screen bracket 516. It is alsopossible for a mixture, where the Primary Guide moves with electronicdisplay 102 and the Secondary Guide is statically mounted to opticsblock 104, and a Secondary Bushing (e.g., C-shaped half bushing 506 b)moves instead.

Further, guiding features could be integrated into display bracket 516,housing 1902 of HMD 101, or optics block 104 directly. FIG. 19A shows aperspective view of guidance channels 1904 with rectangular shaped edgesdesigned to receive guide rails 1906 that are attached to displaybracket 516. As above, guide rails 1906 fit into guidance channels 1904to allow guide rails 1906 to move electronic display 102 back and forthin the z-direction relative to optics block 104, which is fixed, in thisexample, relative to housing 1902 of HMD 101. Similarly, FIG. 19B showsa side-cut view of guidance channels 1904 with rectangular shaped edgesdesigned to receive guide rails 1906 attached to display bracket 516.Features may be designed to offer spring compliance or to remove any fitclearance, for example.

Instead of, or in addition to features or guide pins, pivoting linkagescould be used to constrain or guide motion of electronic display 102relative to optics block 104, in various embodiments. FIG. 20 showsscissor linkage 2002 that constrain or guide motion of electronicdisplay 102 in the z-direction (i.e., optical axis). Here, there are twoscissor linkages 2002; a first scissor linkage that expands horizontally(along x-axis) when compressed and a second linkage that expandsvertically (along y-axis) when compressed to steady movement in thez-direction. One end of each scissor linkage 2002 connects to displaybracket 516 and another end is connected to optics block 104.

Similarly, FIGS. 21A-21B show a Sarrus linkage guidance implementation.FIG. 21A shows compressed state of a Sarrus linkage used to constrain orguide motion of electronic display 102 relative to optics block 104, inone embodiment. In this implementation, the Sarrus linkage includes twoindividual linkages 2100 each composed of two rectangular plates (2102a, 2102 b) with hinge 2104 connecting each rectangular plate (2102 a,2102 b) of the individual linkages.

Accordingly, FIG. 21B shows an expanded state of a Sarrus linkage, inone embodiment. Here, each hinge 2104 from its position shown in FIG.21A and together with its respective rectangular plates (2102 a, 2102 b)makes a circular arc motion that produces linear movement in the zdirection. Thus, each individual linkage 2100 expands (one horizontallyalong x-axis when compressed and the other vertically along y-axis whencompressed) to steady movement of electronic display 102 in thez-direction.

Additionally, the screen flex cable may be modified or redesigned toinclude a region intended for repeated flexing as electronic display 102repeatedly moves back and forth. This could be as simple as making partof it longer, or making the cable two piece. The second piece could benon-flex style, more like a traditional “round” cable. Strain reliefwill be used to protect cable, and isolate IPD from Varifocal flexingportions.

Additional Configuration Information

The foregoing description of the embodiments has been presented for thepurpose of illustration; it is not intended to be exhaustive or to limitthe patent rights to the precise forms disclosed. Persons skilled in therelevant art can appreciate that many modifications and variations arepossible in light of the above disclosure.

The language used in the specification has been principally selected forreadability and instructional purposes, and it may not have beenselected to delineate or circumscribe the inventive subject matter. Itis therefore intended that the scope of the patent rights be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thepatent rights.

What is claimed is:
 1. A varifocal actuation block comprising: anelectronic display of a head mounted display (HMD), the electronicdisplay coupled to a bracket; one or more actuators coupled to theelectronic display of a head mounted display (HMD) and to an opticsblock of the HMD, the one or more actuators configured to move theelectronic display back and forth relative to the optics block, wheremovement of the electronic display relative to the optics block changesa location of an image plane of the electronic display as seen throughthe optics block; a guidance system coupled to the bracket andconfigured to allow movement of the electronic display along an opticalaxis of the optics block while resisting movement of the electronicdisplay along other axes; and an encoder configured to: receive an inputcorresponding to a location for the image plane for a frame of a virtualscene presented on the electronic display; determine a position for theelectronic display relative to the optics block to achieve the locationfor the image plane; and transmit an instruction for the one or moreactuators to move the electronic display relative to the optics block toachieve the location for the image plane for the frame of the virtualscene.
 2. The varifocal actuation block of claim 1, wherein an actuatorof the one or more actuators is mounted to a center of the bracket andbehind the electronic display, and the guidance system comprises: afirst flexure and a second flexure coupled to a back of the electronicdisplay, the first flexure and the second flexure configured to beplanar when no force is applied and patterned to guide movement of theelectronic display along the optical axis of the optics block when forceis applied.
 3. The varifocal actuation block of claim 2, wherein apattern of the first flexure and of the second flexure is configured tooperate a spring bias towards an equilibrium when the first flexure andthe second flexure are flat.
 4. The varifocal actuation block of claim1, wherein the guidance system comprises: a first flexure and a secondflexure coupled to an actuator of the one or more actuators via a powerscrew, the first flexure and the second flexure configured to be planarwhen no force is applied and patterned to guide movement of theelectronic display along the optical axis of the optics block when forceis applied.
 5. The varifocal actuation block of claim 1, wherein theguidance system comprises: a guide pin coupled to the bracket; a guidecoupled to the optics block; and a C-shaped half-bushing coupled to theoptics block into which the guide pin is inserted, the guide and theC-shaped half-bushing configured to allow movement of the electronicdisplay via the guide pin along an optical axis of the optics blockwhile resisting movement of the electronic display along other axes. 6.The varifocal actuation block of claim 1, wherein the guidance systemcomprises: a primary guide pin coupled to the bracket; a secondary guidepin coupled to the bracket; a guide coupled to the optics block, theprimary guide pin inserted into the guide; and a C-shaped half-bushingcoupled to the optics block, the primary guide pin and the secondaryguide pin inserted into the C-shaped half bushing, the secondary guidepin configured to prevent rotation about the primary guide pin.
 7. Thevarifocal actuation block of claim 1, wherein the guidance systemcomprises: a guide pin coupled to the optics block; a guide coupled tothe bracket; and a C-shaped half-bushing coupled to the bracket intowhich the guide pin is inserted, the guide and the C-shaped half-bushingconfigured to allow movement of the electronic display via the guide pinalong an optical axis of the optics block while resisting movement ofthe electronic display along other axes.
 8. The varifocal actuationblock of claim 1, wherein the guidance system comprises: one or moreguidance channels each having rectangular shaped edges configured toreceive guide rails attached to the bracket and configured to allow theelectronic display to move along the optical axis of the optics blockvia the guide rails.
 9. The varifocal actuation block of claim 1,wherein the guidance system comprises: a first scissor linkage with afirst end coupled to the bracket and a second end coupled to the opticsblock, the first scissor linkage configured to expand along a first axisorthogonal to the optical axis of the optics block when compressed; anda second scissor linkage with a third end coupled to the bracket and afourth end coupled to the optics block, the second scissor linkageconfigured to expand along a second axis orthogonal to the optical axisof the optics block and orthogonal to the first axis when compressed.10. The varifocal actuation block of claim 1, wherein the guidancesystem comprises: a first linkage comprising a plurality of rectangularplates connected to each other by one or more hinges, the first linkagecoupled to the optics block and to the bracket and configured to expandalong a first axis perpendicular to the optical axis of the optics blockwhen compressed; and a second linkage comprising an additional pluralityof rectangular plates connected to each other by one or more additionalhinges, the second linkage coupled to the optics block and to thebracket configured to expand along a second axis perpendicular to theoptical axis of the optics block and perpendicular to the first axiswhen compressed.
 11. A head mounted display (HMD) comprising: at leastone processor; an electronic display configured to display a virtualscene to a user wearing the HMD, the electronic display coupled to abracket; an optics block comprising one or more lenses configured tofocus light from the electronic display to an exit pupil of the HMD; anda varifocal actuation block comprising: one or more actuators coupled tothe electronic display and to the optics block of, the one or moreactuators configured to move the electronic display back and forthrelative to the optics block, where movement of the electronic displayrelative to the optics block changes a location of an image plane of theelectronic display as seen through the optics block; a guidance systemcoupled to the bracket and configured to allow movement of theelectronic display along an optical axis of the optics block whileresisting movement of the electronic display along other axes; and anencoder configured to: receive an input corresponding to a location forthe image plane for a frame of a virtual scene presented on theelectronic display; determine a position for the electronic displayrelative to the optics block to achieve the location for the imageplane; and transmit an instruction for the one or more actuators to movethe electronic display relative to the optics block to achieve thelocation for the image plane for the frame of the virtual scene.
 12. TheHMD of claim 11, wherein an actuator of the one or more actuators ismounted to a center of the bracket and behind the electronic display,and the guidance system comprises: a first flexure and a second flexurecoupled to a back of the electronic display, the first flexure and thesecond flexure configured to be planar when no force is applied andpatterned to guide movement of the electronic display along the opticalaxis of the optics block when force is applied.
 13. The HMD of claim 12,wherein a pattern of the first flexure and of the second flexure isconfigured to operate a spring bias towards an equilibrium when thefirst flexure and the second flexure are flat.
 14. The HMD of claim 11,wherein the guidance system comprises: a first flexure and a secondflexure coupled to an actuator of the one or more actuators via a powerscrew, the first flexure and the second flexure configured to be planarwhen no force is applied and patterned to guide movement of theelectronic display along the optical axis of the optics block when forceis applied.
 15. The HMD of claim 11, wherein the guidance systemcomprises: a guide pin coupled to the bracket; a guide coupled to theoptics block; and a C-shaped half-bushing coupled to the optics blockinto which the guide pin is inserted, the guide and the C-shapedhalf-bushing configured to allow movement of the electronic display viathe guide pin along an optical axis of the optics block while resistingmovement of the electronic display along other axes.
 16. The HMD ofclaim 11, wherein the guidance system comprises: a primary guide pincoupled to the bracket; a secondary guide pin coupled to the bracket; aguide coupled to the optics block, the primary guide pin inserted intothe guide; and a C-shaped half-bushing coupled to the optics block, theprimary guide pin and the secondary guide pin inserted into the C-shapedhalf bushing, the secondary guide pin configured to prevent rotationabout the primary guide pin.
 17. The HMD of claim 11, wherein theguidance system comprises: a guide pin coupled to the optics block; aguide coupled to the bracket; and a C-shaped half-bushing coupled to thebracket into which the guide pin is inserted, the guide and the C-shapedhalf-bushing configured to allow movement of the electronic display viathe guide pin along an optical axis of the optics block while resistingmovement of the electronic display along other axes.
 18. The HMD ofclaim 11, wherein the guidance system comprises: one or more guidancechannels each having rectangular shaped edges configured to receiveguide rails attached to the bracket and configured to allow theelectronic display to move along the optical axis of the optics blockvia the guide rails.
 19. The HMD of claim 11, wherein the guidancesystem comprises: a first scissor linkage with a first end coupled tothe bracket and a second end coupled to the optics block, the firstscissor linkage configured to expand along a first axis orthogonal tothe optical axis of the optics block when compressed; and a secondscissor linkage with a third end coupled to the bracket and a fourth endcoupled to the optics block, the second scissor linkage configured toexpand along a second axis orthogonal to the optical axis of the opticsblock and orthogonal to the first axis when compressed.
 20. The HMD ofclaim 11, wherein the guidance system comprises: a first linkagecomprising a plurality of rectangular plates connected to each other byone or more hinges, the first linkage coupled to the optics block and tothe bracket and configured to expand along a first axis perpendicular tothe optical axis of the optics block when compressed; and a secondlinkage comprising an additional plurality of rectangular platesconnected to each other by one or more additional hinges, the secondlinkage coupled to the optics block and to the bracket configured toexpand along a second axis perpendicular to the optical axis of theoptics block and perpendicular to the first axis when compressed.